Linux Network Thread Model

主线程监听请求；
当有请求连接到达时，生成一个子线程处理请求的连接；
子线程连接处理完成时，关闭连接，线程退出；

流程图如下：
Linux Network Thread Model

代码如下：

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <malloc.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <pthread.h>
#include <syslog.h>

#define PORT 80
#define BUFFER_LEN 1UL << 10

typedef struct connection{
    unsigned int fd;
    struct sockaddr_in addr;     
}Connection;

void *request_handler(void *);

int main(void)
{
    struct sockaddr_in server;
    memset(&server, 0, sizeof(struct sockaddr_in));
    
    int listenfd = socket(AF_INET, SOCK_STREAM, 0);
    
    server.sin_family = AF_INET;
    server.sin_port = htons(PORT);
    server.sin_addr.s_addr = htonl(INADDR_ANY);
    
    bind(listenfd, (struct sockaddr *)&server, sizeof(struct sockaddr_in));
    
    listen(listenfd, 255);
    
    syslog(LOG_INFO, "Thread[%ud] is listening on port[%d]......\n", pthread_self(), PORT);
    
    for(;;){
        struct sockaddr_in from;
        socklen_t len = sizeof(struct sockaddr_in);
        memset(&from, 0, sizeof(struct sockaddr_in));
        int connectfd = accept(listenfd, (struct sockaddr *)&from, &len);
        if(connectfd > 0){
            Connection* conn = (Connection *)malloc(sizeof(Connection));
            conn->fd = connectfd;
            conn->addr = from;
            pthread_t *p = (pthread_t *)malloc(sizeof(pthread_t));
            pthread_create(p, NULL, request_handler, conn);
        }
    }
    close(listenfd);
    return 0;
}


void *request_handler(void *args){
    pthread_detach(pthread_self());
    Connection *conn = (Connection *)args;
    syslog(LOG_INFO, "Thread[%ud] is handling request......\n", pthread_self());
    int connectfd = conn->fd;
    struct sockaddr_in from = conn->addr;
    char str[INET_ADDRSTRLEN];
    syslog(LOG_INFO, "receive request from %s %d\n", inet_ntop(AF_INET, &from.sin_addr, str, INET_ADDRSTRLEN), ntohs(from.sin_port));

    char buf[BUFFER_LEN];
    memset(buf, 0, BUFFER_LEN);
    read(connectfd, buf, BUFFER_LEN);
    syslog(LOG_INFO, "The message is : %s\n", buf);
    char* response = "I got your message!\n";
    write(connectfd, response, strlen(response));
    close(connectfd);
    free(conn);
    pthread_exit(NULL);
}

备注说明：

在子线程处理函数void *request_handler(void *args)中，需要将子线程与主线程进行分离操作，即pthread_detach(pthread_self())；否则的话，子线程结束后资源不会被系统自动回收，从而导致thread memory leak;
子线程退出之前，需要关闭connectfd，否则会导致应用程序打开过多的套接字而导致error=24, too many open files.